1. Field of the Invention
The present invention relates to improvements in the use of a high-performance, catalytically activated carbon for the removal of chloramines from chloramine-containing fluid streams. In particular, this application relates to the use of high-performance, catalytically activated carbon filters for the removal of chloramines from chloramine-containing fluid streams wherein the carbon characterized by having present in the graphene structure of the carbon from 0.01 to 10 wt % of aromatic nitrogen species.
2. Description of the Prior Art
While chlorination has made the U.S. water supply safe from illness producing bacteria, viruses, and parasites, an unhealthy by-product of chlorinating water that contains natural organics is the production of trihalomethanes, which have been linked to increased risk of cancer. One way to reduce this risk is to change from chlorine disinfection to chloramine disinfection. Chloramines are formed from the reaction between ammonia and chlorine. Thus, adding ammonia (NH3) to a chlorination system converts chlorine to chloramines. Specifically, monochloramine, hereafter referred to as “chloramine,” in low concentrations arise from the disinfection of potable water sources. To improve the taste and odor of the water and to remove the inherently toxic chloramine, the water is typically contacted with activated carbon. The ability of carbonaceous materials, such as activated carbon, to remove chloramine from aqueous streams is generally well known. It is also known that improvements in removal of chloramine can be achieved by reducing the mean particle diameter of the carbon and by increasing the carbon bed contact time. In some applications, such as in kidney dialysis units, high removal rates of chloramine are particularly important. Although parameters such as contact time and mean particle diameter are known to affect chloramine removal efficiencies, removal performance is neither well understood nor particularly effective.
Activated carbon is used in the treatment of water in the form of powdered activated carbon, granular activated carbon, or shaped activated carbon, such as pellets or spheres. Another form of shaped activated carbon often recommended for point-of-use (POU) and point-of-entry (POE) water treatment, however, is solid block activated carbon. Block activated carbon is a compressed blend of selected activated carbon and a binder material, such as high density polyethylene (HDPE), which is capable of adsorbing a wide range of organic materials. Water is forced through the pores of the densely compacted carbon block, where a combination of mechanical filtration, electrokinetic adsorption, and physical/chemical adsorption takes place to reduce or eliminate a wide range of contaminants.
U.S. Pat. No. 5,338,458, issued on Aug. 16, 1994 to Carrubba et al., titled “Method for Removing Chloramine with Catalytic Carbon,” teaches an improved process for the removal of chloramine from gas or liquid media by contacting said media with a catalytically-active carbonaceous char. In practice, however, a product manufactured according to the patent teaching has been found lacking in effectiveness for chloramine removal from drinking water. Additionally, attempts to replicate even the relatively poor performance of the commercial product based on the '458 patent (Centaur®) in solid block form has not been satisfactory. Apparently, the impact of the binder component detracts measurably from the prior art carbon's performance for chloramine removal.
The applicants' pending application Ser. No. 10/141,158, filed May 8, 2002 teaches an improved method of removal of chloramine from drinking water with an activated carbon that is made catalytically active for removal of chloramines by a process of pyrolyzing the (primarily wood-based) carbon while simultaneously passing a gas stream comprised of a mixture of NH3 and an oxygen-containing gas through the carbon.
Also, the applicants' pending application Ser. No. 10/144,201, filed May 10, 2002 teaches an improved method of removal of chloramine from drinking water with an activated carbon that is made catalytically active for removal of chloramines by a process of pyrolyzing the (primarily wood-based) carbon while simultaneously passing a gas stream comprised of a mixture of NH3 and an oxygen-containing gas through the carbon, wherein the activated carbon is in the form of a solid block.
While the inventions of these prior applications showed great improvement in chloramine removal efficiency over the prior art Centaur® catalytic activated (primarily coal-based) carbons of U.S. Pat. No. 5,338,458, a complete understanding of the reasons for such benefits were not entirely understood. Moreover, it was appreciated that having such understanding could permit controlling the process for treating the activated carbon in a manner to achieve further improved chloramine removal efficiencies and enhanced process productivity.
Accordingly, it is the object of the present invention to provide greater improvements in removal of chloramines from drinking water. It is a further object of the invention to provide an activated carbon that is catalytically active for removal of chloramines apart from factors such as extended contact time, mean particle diameter, and the like which factors are known to affect removal of chloramines. Finally, it is an object of this invention to provide an improved method of chloramines removal using an activated carbon that is catalytically active for removal of chloramines in the form of a solid block activated carbon.